If you'd prefer to carry your gear in a bag rather than stretching out your jersey pockets, Banjo Brothers' Large Seat Bag is perfect for you. It'll hold a tube, tire levers, patch kit, a mini tool, your wallet, some food, even a wind vest or camera (each sold separately). And if you're going big, it expands to haul more gear. It's made from heavy-duty 840-denier nylon with a wide-opening design for easy access. And you've got 360 degrees of visibility with reflective accents and a rear tab for a blinkie.
Capacity: 105-130 cubic inches
Dimensions (unexpanded): 8 x 4.5 x 3.75 inches